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Why does the fuel tank on my 1988 GL 1500 build up so much pressure? Many times I can hear the cap venting with a humming noise. I have a new cap on the tank.

Thanks
 

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Mine does the same thing...it has never been a bother. First time i noticed it, i tore my bike apart looking for the noise. You can imagine what i was thinking after taking off all that tupperware for a frickin gas cap venting. :doh: anyways, it only does it when its hot outside. As for why? Heat expansion in the tank...i think its normal.
 

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I believe it's the heat of the engine directly near the tank. The warmer the engine, the more whoosh when I crack the lid. This past summer it was a habit with me to always crack the cap for a second after a hot ride. If not, mine made funny noises as the pressure built up and escaped.

I too spent a lot of time looking for that funny sound when parked. I though I had something electrical still running, and I was bound to find it, lol.
 

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I understand but why did it begin this last summer? I live 20 miles south of Daytona Beach and originally from north of Atlanta so the summers are similar. Could it be the ethanol or more ethanol in the gas? Keep in mind my bike does not have a hose coming out of the gas cap...
 

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Duckster wrote:
I understand but why did it begin this last summer? I live 20 miles south of Daytona Beach and originally from north of Atlanta so the summers are similar. Could it be the ethanol or more ethanol in the gas? Keep in mind my bike does not have a hose coming out of the gas cap...
Yep ! I think you may be on to something there.....

Mine does it also when really hot and I do a lot of long riding.....and I do have the hose coming out of the top of the gas cap...
 

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Thanks. I thought about drilling a hole in the center of the cap and putting a vacuum line fitting elbow in the hole to allow the pressure to escape. Any thoughts?
 

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If it just started doing this with a new cap, maybe the old cap wasn't sealing, and the pressure just escaped instead of building up? Just throwing this out there.
 

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Duckster wrote:
Thanks. I thought about drilling a hole in the center of the cap and putting a vacuum line fitting elbow in the hole to allow the pressure to escape. Any thoughts?
Your fuel tank was designed to hold a pressure. Why would you want to change that?:?

JD
 

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I just drilled a hole in the cap and was done with it.
 

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Duckster wrote:
Thanks. I thought about drilling a hole in the center of the cap and putting a vacuum line fitting elbow in the hole to allow the pressure to escape. Any thoughts?
You put cold gas in a bike tank over a warm engine and shut thae cap and as the fuel warms it expands. It's not a bad thing. It's normal.

The cap is vented one way only, it let's atmosphere into the tank as the pump removes it while you ride. You pump 5 gallons out in the next 200 miles, something has to take it's place.

You don't want an unchecked open vent to atmoshpere for several reasons like ...you'll smell the strong odor of gasoline ... you'll see gas itself pushed out when near full ... if the bike is dropped it'll spill out ...and an open vented gas tank is like stroring gas in an open dish and certain parts of it will evaporate leaving other parts as a varnish or gum.



:thumbsdown:
 

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The problem started after the carbs were overhauled with in nine months of moving from the metro Atlanta area to just below Daytona Beach. Pressure built up, blew past the fuel auto shut off valve (I had that replaced with a new valve), flooding the engine, and then contaminating the oil of which I changed. Does 87 octane built up pressure faster than 93 octane???
 

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AZgl1500 did you have the same problem with a lot of pressure? What size hole did you drill?

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Dont drill any holes. What you hear is normal. It might be pressure or vacuum. Both are normal. When you use a lot of fuel it can actually develop vacuum in the tank. At other times pressure is built but the cap will vent either when necessary. If you fuel after a long ride where you used a lot of fuel and the tank is near empty that is usually vacuum.
 

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Thanks for all of the information. The noise I hear is a low humming sound and not until after the carbs were overhauled did I notice the noise. Also about the same time I moved to Central Florida was when the carbs were done----along with a new fuel tank and pinion seal.
 

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Others have posted issues with the humming of the fuel cap. Again, that is normal. Aparently the air going by the fuel cap makes something vibrate. Most say it happens when the bike is first turned off. I think that is an indication that the cap seals well and all is working as it should. Relieves when pressure is high enough.
 

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Yes the humming noise begins just after the bike is cut off. It has happened as I was backing the bike into my carport during hot weather here in Central Florida. More so when the tank is full or nearly full. The entire episode has liked to have drove me nuts.
 
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